Plastic liners for controlled fragmentation



G. FOUNTAIN PLASTIC LINERS FOR CONTROLLED FRAGMENTATION Jun. 27, .1970

Filed June 8, 1954 INVENTOR. GILBERT FOUNTAIN 2 1005% ATTORNEYS United States Patent O 3,491,694 PLASTIC LINERS FOR CONTROLLED FRAGMENTATION Gilbert Fountain, China Lake, Calif-, assignor to the United States of America as represented by the Secretary of the Navy Filed June 8, 1954, Ser. No. 435,383 Int. Cl. F42b 13/48, 13/18 US. Cl. 10267 4 Claims The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to explosive munitions of the controlled fragmentation type and more particularly to improvements in the construction of and method of manufacturing explosive munitions utilizing the grooved-charge method of controlled fragmentation.

In the type of munition to which the present invention pertains, it is desirable to effect maximum fragmentation of the casing containing the explosive and to provide for the formation of fragments of substantially equal size. One prior method of achieving this end, commonly referred to as the grooved-charge method of controlled fragmentation, comprises the formation, in the surface of the explosive charge, of a plurality of grooves or recesses of predetermined size, shape, and relative disposition. Upon de onation of the explosive within its casing, the recesses give rise to localized shaped-charge effects which cause fragmentation of the casing into fragments of a size and number deter-mined by the groove or recess pattern.

He eofore, the recess pattern in the explosive surface, for effecting such controlled fragmentation of a metallic casing, was produced by means of a cylindrical mold or liner, of latex rubber, having formed on its inner surface a plurality of solid projections arranged in a desired pattern. The mold was placed in a supporting structure and a liquified explosive material was poured thereinto. Upon solidification of the explosive, a recess pattern, corresponding to the projection pattern on the mold, would be formed in the explosive. Such a rubber mold proved to be unsatisfactory, however, since it did not possess sufficient strength to resist the pressure of the liquid explosive and was deformed under such pressure with the resultant formation, in the explosive, of a deformed recess or groove pattern. Of primary importance, however, was the fact that the wall thickness of such rubber mold was not uniform. Thus, the recess or groove forming projections on the mold were necessarily solid in cross-section since hollow projections, having walls of a thickness equal to that of the mold material i self, would collapse under the pressure head of the liquid explosive. Accordingly, in the prior constructions if the mold were permitted to remain on the explosive charge so as to form a liner and the charge with the liner thereon were placed in the metallic casing, the grooves in the charge would be filled by the solid rubber material forming the projections, and the localized shaped charge effect, which otherwise would be produced by each of the recesses upon detonation of the explosive, would be destroyed or partially neutralized. Attempts to manufacture grooved-charge controlled fragmentation devices by methods which involved the removal of the rubber liner or mold prior to placing of the solidified, grooved explosive charge with its metallic casing proved to be excessively costly and dangerous to practice.

The present invention, which avoids the disadvantages inherent in the prior grooved-charge explosive devices and in the method of producing the same, comprises, in substance, a mold-liner formed of a sheet of relatively rigid plastic or other suitable material which is embossed 3,491,594 Patented Jan. 27, 1970 in a manner to form on one side thereof a series of pro ectrons arranged in a desired pattern. The liner is formed into a cylinder and disposed in the metallic casing comprising the shell of the explosive device after which a liquified explosive is poured into the liner and allowed to solidify. The projections on the liner cause recesses to be formed in the surface of the solidified explosive. Because of the increased strength of the plastic material forming the liner, the projections embossed in the latter may be relatively thin-walled whereby to provide a liner of uniform thickness with hollow projections which do not adversely affect the shaped-charge effects produced by the recesses in the surface of the explosive and, accordingly, it is not necessary that the liner be removed from the explosive charge.

In accordance with the foregoing, an object of the present invention is the provision of an improved controlled fragmentation explosive device and method of making same.

Another object of the invention is to provide an improved explosive device utilizing the grooved-charge method of controlled fragmentation and improved method of making the same.

A further object of the invention is the provision of an improved controlled fragmentation explosive device and an improved method of making he same, as in the foregoing, wherein a relatively thin, relatively rigid plastic liner, having a desired groove or recess-forming pattern embossed therein, is disposed within a metallic shell comprising the casing of the explosive device, and wherein further a liquified explosive material is poured into the liner, the recess-forming pattern on the liner causing a corresponding recess pattern to be formed in the surface of the explosive upon solidification of the latter.

Other objects and advantages of the present invention will become apparent as the same becomes better understood from. the following detailed description had in conjunction with the annexed drawings wherein:

FIG. 1 is a plan view of a portion of the groove forming liner of the present invention;

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1;

FIG. 3 is a cross-section of an explosive construction 1ncorporating the features of the present invention;

FIG. 4 illustrates a modified liner; and

FIG. 5 is a cross-section of an explosive construction incorporating the modified liner of FIG. 4.

Referring now to the drawings and more particularly to FIGS. 1 and 2 thereof, the liner of the present invention, for effecting controlled fragmentation of an explosive device, comprises a relatively thin sheet 10, of a plastic or other suitable material, having formed in one side thereof a plurality of V-shaped indentations 11 which result in the raising, on the other side of the sheet 10, of a plurality of substantially V-shaped, thin-walled projections 12. Sheet 10 is com rised of some suitable material, as for example a plastic material such as cellulose triacetate, which is capable of withstanding, without appreciable deformation of the indentations formed therein, temperatures up to approximately 200 F. The indentations 11 and resultant projections 12 are arranged in a predetermined pattern, such as the checkerboard pattern illustrated, to effect desired fragmentation as will hereinafter appear. Adjacent each of two opposed edges of sheet 10 is formed an elongated U- or V-shaped channel 13 and 14 (see FIG. 3), which channels extend the entire length of sheet 10 and which are for a purpose to be later described. In the alternative arrangement shown in FIGS. 4 and 5, the liner 10' may have fiat opposed edge portions 13 as illustrated and a channel 14', extending the length of the liner, adjacent portion 13'. The flat edge portions and channel are for a purpose described below. In the manufacture of the present explosive device, the liner is formed into a generally cylindrical shape with channels 13 and 14 disposed in overlapping relationship, if the liner of FIGS. 1 through 3 is employed, or with the flat edge portions 13 disposed in overlapping relationship, if the modified liner of FIGS. 4 and 5 is employed, The overlapping portions may then be sealed together as by heat welding or adhesive bonding. The resultant cylindrical liner is positioned within the cylindrical metallic shell 15, which may comprise the casing of a fragmentation rocket, for example, andd an explosive composition 16, which in one phase of its preparation is in a liquid state, is poured into the shell 15 so as to fill the volume defined by the liner or 10. The liner 10 or 10' functions as a mold element whereby upon solidification of the explosive composition 16 there will be formed in the surface of the latter a plurality of V- shaped grooves or recesses 17 arranged in a pattern conforming to that on the liner. Overlapping channels 13 and 14, in the liner of FIGS. 1 through 3, and the single channel 14, in the modified liner of FIGS. 4 and 5, permit. compensation for the manufacturing tolerances in the internal diameter of the metallic casing 15 by virtue of the resilience of the continuous longitudinal channel as distinguished from the rigidity of the checkerboard type construction of the remainder of the liner, whereby any given liner may be caused to have a snug fit within any given casing. Thus, the cylinder into which the liner is formed, as set forth above, is made to have a diameter slightly greater than the internal diameter of the metallic casing 15. Radial pressure is then applied to the cylindrical liner in such a manner as to resiliently force the sides of the overlapping channels 13 and 14 or channel 14' toward each other whereby to reduce the diameter of the lier sufiiciently to enable it to be slidably inserted into the metallic casing. After insertion of the liner into the casing, the sides of the overlapping channels 13 and 14 or channel 14' will tend to spring back to their original position whereby the surface of the liner will be urged into intimate contact with the inner surface of the casing. Such intimate contact of the outer liner surface with the inner casing surface is desirable in order to prevent leakage of liquified explosive material between the liner and casing during the pouring of the explosive material into the liner.

Fragmentation control in the instant explosive construction results from the formation, during detonation, of localized shaped-charge effects adjacent to each of the V-shaped grooves formed in the surface of the explosive charge 16. Thus, it was discovered, prior to this invention, that the inclined side Walls of such a groove caused localized concentration of the explosive shock wave with the resultant formation of a concentrated shock force of increased magnitude directed along a radial plane passing through the apex of the groove. When, as in the present invention, the charge is provided with a plurality of grooves arranged in a predetermined pattern, such as the checkboard pattern illustrated and is disposed within a metallic casing, the several shapedcharge elfects, resulting from the several grooves, cause fragmentation of the casing along lines defining the intersection of the casing and the aforesaid radial planes of shock wave concentration. Accordingly, the casing may be caused to fragmentate into pieces of desired shape, size, and number by proper selection of groove pattern and groove configuration.

As heretofore set forth, prior methods of fabricating explosive constructions utilizing a grooved-charge for effecting controlled fragmentation involved the use of a latex rubber liner having a desired groove-forming pattern thereon. It was, however, necessary, in such prior fabrication methods, to remove the liner prior to insertion of the explosive charge into the metallic casing comprising the construction since the groove-forming projections on the liner were necessarily solid in cross-section and would, if the liner were permitted to remain on the charge, result in the grooves in the latter being filled by latex rubber material, and the shaped-charge effects of the grooves would, thereby, be substantially reduced or completely destroyed. In the present invention, however, the wall thickness of the liner may be made uniform owing to the increased strength of the plastic material from which the liner is made; that is, the groove-forming projections 12 may comprise thin walls of the same thickness as the liner itself, and, as a result, the liner does not interfere with or prevent the formation of shock wave concentrations. It will be seen, therefore, that the present liner may remain on the explosive charge without adverse elfect on fragmentation control whereby the present method of making a controlled fragmentation explosive device is safer and more economical to practice than prior fabrication methods.

What is claimed is:

1. A controlled fragmentation explosive device comprising a cylindrical metallic fragmentation casing, a cylindrical mold member of relatively thin resilient material and of an uncompressed normal outer diameter slightly greater than the inner diameter of said casing, said mold member being disposed within said casing with the outer wall of the mold member resiliently pressed against and engaging the inner wall of said casing, said mold member having a plurality of indentations formed in its outer surface in a predetermined pattern and corresponding raised portions on the inner surface of said mold member, and a solidified explosive filling said mold member.

2. The arrangement according to claim 1 wherein said material is a relatively hard and heat resistant plastic.

3. The arrangement according to claim 1 wherein said indentations and corresponding raised portions are substantially V-shaped in cross-section.

4. The arrangement according to claim 1 wherein said mold member has formed therein a channel extending the length thereof, the walls of said channel being adapted to be sprung together upon insertion of the mold member into the casing whereby when said last mentioned walls spring apart, the outer surface of the mold member will be urged into tight engagement with the inner wall of the casing.

References Cited UNITED STATES PATENTS 2,195,429 4/1946 Shaler 86-20.5

FOREIGN PATENTS 692,741 6/1953 Great Britain. 438,053 7/ 1948 Italy. 369,237 3/ 1939 Italy. 843,734 4/1939 France. 1,077,997 5/ 1954 France.

BENJAMIN A. BORCHELT, Primary Examiner US. Cl. X.R. 1025 6 

1. A CONTROLLED FRAGMENTATION EXPLOSIVE DEVICE COMPRISING A CYLINDRICAL METALLIC FRAGMENTATION CASING, A CYLINDRICAL MOLD MEMBER OF RELATIVELY THIN RESILIENT MATERIAL AND OF AN UNCOMPRESSED NORMAL OUTER DIAMETER SLIGHTLY GREATER THAN THE INNER DIAMETER OF SAID CASING, SAID MOLD MEMBER BEING DISPOSED WITHIN SAID CASING WITH THE OUTER WALL OF THE MOLD MEMBER RESILIENTLY PRESSED AGAINST AND ENGAGING THE INNER WALL OF SAID CASING, SAID MOLD MEMBER HAVING A PLURALITY OF INDENTATIONS FORMED IN ITS OUTER SURFACE IN A PREDETERMINED PATTERN AND CORRESPONDING RAISED PORTIONS ON THE INNER SURFACE OFSAID MOLD MEMBER, AND A SOLIFIED EXPLOSIVE FILLING SAID MOLD MEMBER. 